818 



SUBCLAVIAN ARTERIES. 



in operations upon the larger blood-vessels, 

 the touch often fails to discriminate the pro- 

 per object, the characteristic pulsation of a 

 large artery being, under such circumstances, 

 often wanting. 



In the postero-inferior triangle of the neck 

 the artery is covered by the integument, su- 

 perficial fascia and platysma, descending su- 

 perficial (supra-clavicular) twigs of the cervical 

 plexus, and by the external jugular vein. The 

 situation of this vein in the supra-clavicular 

 space, is subject to much variety ; it most fre- 

 quently runs near to the inner boundary of 

 the triangle and parallel to the outer edge of 

 the sterno-mastoid muscle, but frequently de- 

 scends in the very centre of the space ; in the 

 latter case it much embarrasses the operator 

 in attempting to expose the subclavian artery. 



Next in order, a number of conglobate 

 glands, and a plexus of anastomosing veins, 

 principally from the scapular region, come into 

 view; these latter usually communicate with 

 the external jugular, or with the subclavian 

 vein. Areolar tissue which presents a laminated 

 arrangement encloses these glands and super- 

 ficial vessels, and isolates them from the 

 deeper-seated parts. 



These structures being removed, the sub- 

 clavian artery appears to lie within a second 

 triangle of smaller dimensions, bounded inter- 

 nally by the scalenus anticus muscle, externally 

 and superiorly by the omo-hyoid muscle, and 

 inferiorly by the first rib; this bone represents 

 the base of the triangle, and over it the artery 

 is seen to pass. At this depth, two collateral 

 arterial branches of considerable size cross 

 the supra-clavicular space, the one, the trans- 

 versalis colli, above, the other, the supra- 

 scapular, below the level of this portion of the 

 subclavian artery ; the latter is placed under 

 cover of the clavicle, and in contact with the 

 front of the subclavian vein. As the supra- 

 scapular artery pursues its course towards the 

 shoulder, it crosses in front of the subclavian 

 artery and of the brachial plexus of nerves. 

 Here likewise the clavicle and the subclavius 

 muscle constitute additional anterior relations 

 of the subclavian artery, now near its termi- 

 nation. 



The nervous bundle of the brachial plexus is 

 parallel to the subclavian artery in its third 

 stage, and lies superior and external to the 

 vessel ; in its descent the lower division of 

 the plexus overhangs the artery, and one or 

 two of the branches (anterior thoracic) cross 

 the anterior surface of the artery, and some- 

 times even encircle it in a nervous loop. 



The anterior relations of the third stage of 

 the subclavian artery may therefore be thus 

 arranged : 



1. Integument, superficial cutaneous nerves, 

 platysma, fascia. 



2. Areolar tissue in layers, glands, external 

 jugular vein, an intricate plexus of smaller 

 veins. 



3. Anterior thoracic branches of the bra- 

 chial plexus, the subclavian vein, supra-sca- 

 pular artery, clavicle, and subclavius muscle. 



Anomalies in the origin of the subclavian ar- 



teries. 1. The right subclavian artery some- 

 times arises separately from the arch of the 

 aorta, in which case there is no arteria inno- 

 minata ; the branches that arise from the arch 

 of the aorta are then four in number, but con- 

 siderable variety has been observed in the 

 relation which the right subclavian bears to 

 the other three branches ; thus, 



a. It may occupy the usual position of the 

 innominate artery, being the first in order of 

 the branches of the arch of the aorta ; its re- 

 lations within the thorax will then correspond 

 with those assigned to the vessel whose place 

 it comes to occup}'. 



b. It may be the second in numerical order 

 of the branches of the arch, arising after the 

 right carotid artery, behind which it subse- 

 quently passes to arrive at its proper position 

 in the neck. 



c. It may arise after the two carotids as the 

 third branch of the arch ; or, 



d. It may be the last branch of the aorta, and 

 occupy the usual situation of the left sub- 

 clavian artery. Of the varieties already men- 

 tioned, this is the most frequently met with, 

 and, according to the statistics of Pro- 

 fessor Quain, it occurs once in every 250 

 examinations. 



e. Sometimes (but much more rarely) this 

 vessel arises below the arch, from the thoracic 

 aorta, and its position may be so low, that it 

 will furnish some of the upper intercostal 

 arteries. 



The course of the artery, when it thus arises 

 from the left of the arch, is very remarkable ; 

 it crosses in front of the spinal column, either 

 behind the oesophagus, or between that tube 

 and the trachea, and necessarily passes across 

 the neck behind all the other branches given 

 off from the arch of the aorta. When thus ab- 

 normal ly situated behind the oesophagus, it 

 has been accidentally wounded by a foreign 

 body which had first transfixed that tube. A 

 remarkable example of this occurrence is 

 mentioned by Mr. Kirby, in the 2d vol. of the 

 Dublin Hospital Reports. 



The irregularity in question, of the right 

 subclavian arter}', was regarded by Dr. Bay- 

 ford as the cause of difficult deglutition, in a 

 case which had been accurately observed for 

 many years, and this new disease, as he con- 

 sidered it, he quaintly termed " Dysphagia. 

 lusoria." * 



In those instances, where the right sub- 

 clavian artery has been found to deviate thus 

 strangely from its usual course, the inferior 

 laryngeal nerve presented a remarkable change 

 of direction, depending no doubt on the altered 

 course of the artery ; in all the instances 

 which were noted, the nerve was given off 

 from the pneumogastric, higher up than usual, 

 and passed directly to the larynx, so as not to 

 be entitled to the name of " recurrent." Dr. 

 Hart, who first directed attention to this fact, 

 has thus clearly explained the connection be- 

 tween the unusual position of the artery and 



* Memoirs of the Medical Society of London, 

 vol. ii. 1793. 



